.\" Copyright (c) 1986 Regents of the University of California.
.\" All rights reserved.  The Berkeley software License Agreement
.\" specifies the terms and conditions for redistribution.
.\"
.\"	@(#)icmp.4p	6.1 (Berkeley) 5/16/86
.\"
.TH ICMP 4P "May 16, 1986"
.UC 6
.SH NAME
icmp \- Internet Control Message Protocol
.SH SYNOPSIS
.B #include <sys/socket.h>
.br
.B #include <netinet/in.h>
.PP
.B s = socket(AF_INET, SOCK_RAW, proto);
.SH DESCRIPTION
ICMP is the error and control message protocol used
by IP and the Internet protocol family.  It may be accessed
through a \*(lqraw socket\*(rq for network monitoring
and diagnostic functions.
The
.I proto
parameter to the socket call to create an ICMP socket
is obtained from
.IR getprotobyname (3N).
ICMP sockets are connectionless,
and are normally used with the
.I sendto 
and
.I recvfrom 
calls, though the
.IR connect (2)
call may also be used to fix the destination for future
packets (in which case the 
.IR read (2)
or
.IR recv (2)
and 
.IR write (2)
or
.IR send (2)
system calls may be used).
.PP
Outgoing packets automatically have an IP header prepended to
them (based on the destination address).
Incoming packets are received with the IP header and options intact.
.SH DIAGNOSTICS
A socket operation may fail with one of the following errors returned:
.TP 15
[EISCONN]
when trying to establish a connection on a socket which
already has one, or when trying to send a datagram with the destination
address specified and the socket is already connected;
.TP 15
[ENOTCONN]
when trying to send a datagram, but
no destination address is specified, and the socket hasn't been
connected;
.TP 15
[ENOBUFS]
when the system runs out of memory for
an internal data structure;
.TP 15
[EADDRNOTAVAIL]
when an attempt is made to create a 
socket with a network address for which no network interface
exists.
.SH SEE ALSO
send(2), recv(2), intro(4N), inet(4F), ip(4P)
